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I live near one nuclear plant and drive past another on the way to work every day. For a while my circle of friends included a lot of folks working at both plants -- obviously Homer Simpson is not representative of nuclear power workers and I don't think he actually exists and works at a nuclear power plant, but he's not *that* far off from the worst people on the worst days. You can't eliminate the human factor -- question is whether you can build enough layers of checks and balances so that the worst case result is acceptable.

Fukushima was probably a pretty fair "worst case we're likely to see in a few lifetimes" as long as all the plant maintenance is no worse and the civil response plans and execution are equally good everywhere in the world -- do you believe that is the case ?

You need to understand the real and huge difference from Fukushima 1960s design gen ii nuclear reactor and a Westinghouse AP1000 (gen iii+).
AP1000 can shutdown safely and cooldown for 3 days without any power or any external water. It shutdown automatically if it looses electricity (eletromagnetic locks that close the control rods in case of loss of electricity).
In 3 days is just needs topping off a large water reserve tank, which can be accomplished with a 15hp water pump in a day or a fire fighter pumping car available for an hour. In a month its cool enough it needs no additional care to prevent overheating.
So new reactors are passively safe.

Then there is the final step to making nuclear fission really 99.9999999999% safe. It's shifting from high pressure water as coolant to something that is solid at ambient pressure and only becomes a liquid at temperatures like 400C (750F). Low pressure core + coolants that want to be a solid means even if the nuclear plant is blown to pieces (comet strike or military precision strike with a bunker buster bomb) radioactive materials won't go far perhaps no further than 100ft, and radioactive materials won't vaporize.
The molten salt reactor experiment (MSRE) done in the 60s/70s at ORNL showcased a reactor that was truly walk away safe, not just shutting down by itself like the AP1000, but needing no external power for cooldown and having FLiBe coolant (Lithium Fluoride + Berrylium Fluoride), so there was absolutely nothing that had to be done by the operators in case of an accident, operators where there for normal/slightly abnormal conditions, in case something happened serious enough they could just walk away without fear of being needed to perform any action.

So you see, even your friends that work at a nuclear plant are educated in the reactor they operate, they are very skilled to explain the risks of that technology, and they certainly understand far more about that reactor than I ever will. But I invested hundreds of hours of my personal time understanding nuclear technology at a broader level, and I'm convinced we need to get rid of all coal electricity with nuclear ASAP, even though I'm not a big fan of any water cooled reactor, although an AP1000 and similar competitors are more than so safe I would be fine living right at the outside perimeter of such a nuclear site (with only gen iii+ reactors).

And we need to take molten salt reactors seriously. The very little money spent on molten salts was cancelled because the political favorite was sodium fast breeder reactors. There is a very comprehensive video about this on youtube:https://www.youtube.com/watch?v=bbyr7jZOllI

There is even White House tapes showing how clearly President Nixon wanted Sodium Fast Breeders (and was willing to throw as many billions on that as desired, he clearly states he doesn't care about budget overruns). Then came Three Mile Island, and a coordinated missinformation offensive told the world nuclear was "nasty, wicked and evil" and was a bad idea, while in the meantime coal killed hundreds of thousands yearly worldwide, and TMI killed nobody.

I took the intro course after having studied radiation and nuclear technology for about 18 months using less formal sources.
I got an A+ grade (78 of 80 questions answered right).
The main reason I got that course was so people couldn't criticize me for talking about nuclear technology with information from youtube and wikipedia, and now I'm still an idiot. Please take the class before disqualifying the class and my nuclear education.

Still there's a difference between having taken a crash course into nuclear technology, and having a PhD in nuclear physics or having written a MD doctoral thersis about Rad poisoning. Or just having studied Physics and/or Medicine at the university.
Yes, you probably now a bit better than most clueless netizens.
No, that doesn't make you an instant expert on the subject.
(Disclaimer: Neither am I)

Originally Posted by macpacheco

So new reactors are passively safe.

Yeah basically, the current tendency is to move away from earlier designs, and try to do designs that can take care of themselves in case of problems.
That more or less linked into a change of mentality from cold era (Over simplifying: We need a technology to refine uranium and nuke power is a good pretext! we need to produce plutonium, as fast as possible! we must quickly hack/cobble a civialian nuke technology for that as fast as possible, before the other side does it first and use the technology to build secret nuke weapons before us!) into a more modern approach (over simplifying: Maybe we should be building things that can catastrophically fail as soon as you look at them in a funny way. Perhaps you should take time to design something whose failure mode are safer than biblical plagues).
Still we're using a technology whose legacy had a lot do to with "being ready to make nuke" in addition to "produce power", while having completely overlooked other technology like thorium, etc.
There's still a rational behind keeping uranium (we have a lot of experience with it while alternative are less known technology as it was a lot less experimented with). But there are a lot of missed opportunity at looking at alternative (that were overlooked historically, for lacking any collateral military applications).
Sorry, I'm digressing about human nature and driving away your discussion from reactor technology generations.

@macpacheco: And again you are totally ignoring the human factor. What about greedy companies that use low grade materials to save some money? What about the highly qualified worker that wants to blow up the world because his wife left him? Or having a secret drug problem? Or a sleeper terrorist?
I can think about a thousand scenarios where safety measures will be intentionally disabled to safe money, out of malice or simply out of stupidity. Of course the same can happen at a dam. Or at a coal power plant. But that doesn't make nuclear power any safer.

And of course, as bridgman already pointed out, there is the problem of nuclear waste, which is still not solved.

Still there's a difference between having taken a crash course into nuclear technology, and having a PhD in nuclear physics or having written a MD doctoral thersis about Rad poisoning. Or just having studied Physics and/or Medicine at the university.
Yes, you probably now a bit better than most clueless netizens.
No, that doesn't make you an instant expert on the subject.
(Disclaimer: Neither am I)

Yeah basically, the current tendency is to move away from earlier designs, and try to do designs that can take care of themselves in case of problems.
That more or less linked into a change of mentality from cold era (Over simplifying: We need a technology to refine uranium and nuke power is a good pretext! we need to produce plutonium, as fast as possible! we must quickly hack/cobble a civialian nuke technology for that as fast as possible, before the other side does it first and use the technology to build secret nuke weapons before us!) into a more modern approach (over simplifying: Maybe we should be building things that can catastrophically fail as soon as you look at them in a funny way. Perhaps you should take time to design something whose failure mode are safer than biblical plagues).
Still we're using a technology whose legacy had a lot do to with "being ready to make nuke" in addition to "produce power", while having completely overlooked other technology like thorium, etc.
There's still a rational behind keeping uranium (we have a lot of experience with it while alternative are less known technology as it was a lot less experimented with). But there are a lot of missed opportunity at looking at alternative (that were overlooked historically, for lacking any collateral military applications).
Sorry, I'm digressing about human nature and driving away your discussion from reactor technology generations.

Plutonium produced by commercial reactors is useless for making bombs. Pu-240 contamination leads to serious risks of weapon premature detonation (spontaneous fission). Plus spontaneous fission when it doesn't cause pre detonation, it degrades the other weapons components, so even if a pre detonation doesn't happen you are still risking making your weapon a dud.

Weapons grade plutonium is produced by irradiating a lot of U-238 with low grade neutron sources to avoid having the same U-238 atom from getting two neutrons, this is impossible in the core of any commercial nuclear reactor. But today making bombs doesn't require even making plutonium, new atomic weapons are being built with highly enriched U-235, enrichment is much cheaper than making plutonium.

BTW, Thorium reactors don't make materials suitable for nuclear weapons, U-233 gets contaminated with U-232 which offers the same risks of Pu-240 contamination even at lower concentrations, there is no known U-233 powered weapon in the world's nuclear arsenal, building from U-235 much easier.

Also see James Conca's How Deadly is Your Kilowatt?
As an aside, the 0.04 nuclear deaths /TWh assumes LNT (linear, no threshold) holds and that about 4,000 -- 9,000 people will eventually die over 50 years from increased cancers -- 80 - 180/yr. However, this LNT extrapolation goes right to zero, and includes people who received or will receive lifetime radiation exposure from the Chernobyl accident less than that of lifetime background radiation in many parts of the world (Dr. Zbigniew Jaworowski 2006, reproduced in Chernobyl,The Fear of the Unknown. Flame alert: Atomic Insights is not a universally popular blog. Nonetheless, in 2012 the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 2012) submitted the report that, among other things, states that uncertainties at low doses are such that UNSCEAR “does not recommend multiplying low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or below natural background levels.” (UNDOC/V1255385). In other words, the 4,000 - 9,000 Chernobyl death guestimate was arrived via invalid application of LNT. (From Radiation Is Not A Big Deal - UNSCEAR (a title I personally think could benefit from some of the qualification Conca later provides in the body of the article).

"In terms of effects from radiation exposure immediately after the accident, results of measurements conducted so far by the government of Fukushima Prefecture on tens of thousands of people have shown that the committed dose is less than 1 mSv in more than 99.9% of such people, and the maximum dose observed in this group is as low as the global average background radiation level (2.4 mSv a year)."

Don't get me wrong: in large doses radiation can be deadly and safeguards must be maintained. Some 9,000 people die from skin cancers in the United States alone, each year. (Yet PV remains unfathomably popular </irony>.)

Those who insist that nuclear power be demonstrably 100% safe hold that technology to a far higher standard than any realistically possible alternative. Though cancer is particularly unpleasant, so are the respiratory, hormonal, and immune failures associated with coal, gas, and biofuels. After a certain point a death is a death. How many billions will unpleasantly die as consequence of global warming? How might those be averted?
l

Also see James Conca's How Deadly is Your Kilowatt?
As an aside, the 0.04 nuclear deaths /TWh assumes LNT (linear, no threshold) holds and that about 4,000 -- 9,000 people will eventually die over 50 years from increased cancers -- 80 - 180/yr. However, this LNT extrapolation goes right to zero, and includes people who received or will receive lifetime radiation exposure from the Chernobyl accident less than that of lifetime background radiation in many parts of the world (Dr. Zbigniew Jaworowski 2006, reproduced in Chernobyl,The Fear of the Unknown. Flame alert: Atomic Insights is not a universally popular blog. Nonetheless, in 2012 the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 2012) submitted the report that, among other things, states that uncertainties at low doses are such that UNSCEAR “does not recommend multiplying low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or below natural background levels.” (UNDOC/V1255385). In other words, the 4,000 - 9,000 Chernobyl death guestimate was arrived via invalid application of LNT. (From Radiation Is Not A Big Deal - UNSCEAR (a title I personally think could benefit from some of the qualification Conca later provides in the body of the article).

Don't get me wrong: in large doses radiation can be deadly and safeguards must be maintained. Some 9,000 people die from skin cancers in the United States alone, each year. (Yet PV remains unfathomably popular </irony>.)

Those who insist that nuclear power be demonstrably 100% safe hold that technology to a far higher standard than any realistically possible alternative. Though cancer is particularly unpleasant, so are the respiratory, hormonal, and immune failures associated with coal, gas, and biofuels. After a certain point a death is a death. How many billions will unpleasantly die as consequence of global warming? How might those be averted?
l

Only fools would advocate totally removing nuclear power safety safeguards.
What I and many with PhDs are advocating is radiation safety standards were devised back when the only data points we had were from Hiroshima and Nagasaki and nothing else. Further data points collected over the last 50 years take much of the uncertaintly in the LNT interpolation and show that at a minimum there is a lower safe radiation level. Yet every nuclear accident showed us radiation was less dangerous in low to medium doses than predicted, yet standards were never recalculated.
When a nuclear power plant site is decommissioned, radiation levels are required to return to an insanely low radiation level that requires billions in decontamination, because nuclear operators are forbidden from returning the site to Denver / Salt Lake City levels of radiation (which we know are safe) instead of returning to radiation levels that match the vicinity.
That actually is one of the bottom lines, if radiation safety standards had any logic, then nobody should be allowed to live in Denver or SLC, and heaven forbid even higher cities like 10000 ft sky resort cities, plus nobody should be allowed to live close to large monazite sand areas, there is a city population 200,000 just one hour from my residence, people there are subject to higher levels of radiation than a nuclear worker is allowed to (nuclear worker radiation standards are much higher than the general population). Yet nuclear workers show no higher rates of cancer than the general population from the same city.